Fluorescence bioimaging based on rare-earth-doped nanocrystals (RENCs) in the shortwave infrared (SWIR, 1000–3000 nm) region has aroused intense interest due to deeper penetration depth and clarity. However, their downshifting emission rarely shows sufficient brightness beyond 1600 nm, especially in NIR-IIc. Here, we present a class of thulium (Tm) self-sensitized RENC fluorescence probes that exhibit bright downshifting luminescence at 1600–2100 nm (NIR-IIb/c) for in vivo bioimaging. An inert shell coating minimizes surface quenching and combines strong cross-relaxation, allowing LiTmF₄@LiYF₄ NPs to emit these intense downshifting emissions by absorbing NIR photons at 800 nm (large Stokes shift ~1000 nm with a absolute quantum yield of ~14.16%) or 1208 nm (NIR-II_in and NIR-II_out). Furthermore, doping with Er³⁺ for energy trapping achieves four-wavelength NIR irradiation and bright NIR-IIb/c emission. Our results show that Tm-based NPs, as NIR-IIb/c nanoprobes with high signal-to-background ratio and clarity, open new opportunities for future applications and translation into diverse fields.

由于更深的穿透深度和清晰度，基于短波红外（SWIR，1000-3000 nm）区域的稀土掺杂纳米晶体（RENC）的荧光生物成像引起了人们的强烈兴趣。然而，它们的降档发射很少显示出超过 1600 nm 的足够亮度，尤其是在 NIR-IIc 中。在这里，我们提出了一类铥 (Tm) 自敏 RENC 荧光探针，该探针在 1600–2100 nm (NIR-IIb/c) 处表现出明亮的下移发光，用于体内生物成像。惰性壳涂层最大限度地减少了表面淬火并结合了强交叉弛豫，允许 LiTmF ₄ @LiYF ₄ NPs 通过吸收 800 nm 的 NIR 光子（大 Stokes 位移 ~1000 nm，绝对量子产率 ~14.16%）来发射这些强烈的降档发射) 或 1208 nm (NIR-II _in和 NIR-II_输出）。此外，掺杂 Er ³⁺用于能量捕获实现了四波长 NIR 辐射和明亮的 NIR-IIb/c 发射。我们的研究结果表明，基于 Tm 的 NPs 作为具有高信号背景比和清晰度的 NIR-IIb/c 纳米探针，为未来的应用和转化为不同领域开辟了新的机会。